The subject matter disclosed herein relates generally to radiation detectors and more specifically to radiation detectors for medical imaging, such as Nuclear Imaging (NI), Single Photon Emission Computed Tomography (SPECT), Positron Emission Tomography (PET) and Computed Tomography (CT).
Room temperature pixelated radiation detectors made of semiconductors, such as Cadmium Zinc Telluride (CdZnTe or CZT) semiconductors, have entered into the commercial phase in medical imaging. In this commercial phase, it is desirable for these detectors to exhibit high performance, especially with respect to energy resolution and sensitivity. In addition, these detectors, which are often the core technology integrated into camera heads of systems such as SPECT, PET and CT, should be stable, reliable and produced with high yield to reduce cost.
The radiation semiconductor detectors generally include two surfaces, one having a cathode monolithic electrical-contact applied thereto and another having surface pixelated anodes electrical contacts applied thereto. Prior to the application of the electrical contacts, the first and the second surfaces are etched by chemical wet etching. In CZT radiation detectors, the wet etching is done for at least two reasons: 1) to remove the mechanical damage from the surfaces introduced in previous fabrication steps where the semiconductor wafers of the detectors have been sliced and polished and 2) to create surfaces, which are tellurium rich, which is used to produce Ohmic contacts such as Indium contacts applied to CZT wafers.
The tellurium rich first surface on which the anodes contacts are applied have gap regions between the anodes contacts. The excess tellurium in the regions between the anodes causes these gaps to be of a relatively low surface resistance, which is also instable. The instability results in a reduction in the detector performances such as energy resolution and sensitivity, fabrication with relatively low production yield resulting in high cost detectors and unstable detectors with reduced reliability having quality degradation over time.